Method and apparatus for making high pressure mercury vapor lamps



Jan. 10, 1956 c. KENTY ET AL METHOD AND APPARATUS FOR MAKING HIGH PRESSURE MERCURY VAPOR LAMPS Filed June 4, 1952 Inventors;

Carl Kenty, MDaniel ALarson, Their Attorney United States Patent 2,730,424 METHOD AND APPARATUS FOR MAKING HIGH PRESSURE MERCURY VAPOR LAMPS Carl Kenty, Cleveland Heights, and Daniel A. Larson, Euclid, Ohio, assignors to General Electric Company, a corporation of New York Application June 4, 1952, Serial No. 291,748 3 Claims. (Cl. 316-26) The present invention relates to a method and an apparatus useful in' the manufacture of high pressure mercury vapor discharge lamps.

In the manufacture of elongated high pressure mercury vapor discharge lamps, that is mercury vapor discharge lamps operating with a constricted discharge, it is difficult to make the envelopes of the lamps identical, that is, with exactlythe same volume and having the same shape at their ends and to mount the electrodes in each of the envelopes in exactly the same position with respect to the ends. This is particularly true when the envelopes are of quartz because of the ditiiculty of working quartz to conform to exact specifications.

The volume of the envelopes, the shape of their ends and the position of the electrodes therein determine the pressure of the mercury vapor atmosphere in the envelopes during operating of the lamps which in turn determines the operating electrical characteristics of the lamps. It is,'of course, highly desirable for purposes of designing the lamp ballast equipment to produce lamps I having electrical characteristics, specifically an operating voltage, within close limits. The difficulties of producing such lamps increase as the lamps become smaller in size because the effect of small variations in the above physical features on the vapor pressure and thus on the operating voltage of the lamps is much more pronounced in lamps of small size.

Lamp ballast equipment to provide a narrow range of operating voltages is less expensive than such equipment providing a wide range of such voltages so that the production of lamps each having an operating voltage within a narrow range would etfect important savings in materials and cost of manufacture of the ballast equipment.

In spite of the utmost efiorts to produce lamps having identical physical features and the most accurate control of the amount of liquid mercury introduced into the lamp envelopes during manufacture of the lamps, the shrinkage, that is, the number of completed lamps rejected after final testing, is substantial. About 3% of the lamps of a certain type are rejected because the operating voltage thereof is outside the limits of the operating voltage provided by the commercial ballast equipment for such lamps.

It has been proposed to introduce the mercury in vapor form into the lamp envelope while the lamp is operating and until the increasing mercury vapor pressure in the lamp envelope raises the operating voltage of the lamp to a desired predetermined value. This proposal has not been followed in practice, however, be-

cause of practical difficulties in accurately controlling the rate of flow of the mercury vapor into the lamp envelope and in preventing the escape of mercury vapor from and advantages of the invention will appear from the following detailed description of the species thereof.

According to the invention, the rate of flow of the mercury vapor into the lamp envelope is accurately c0ntrolled by controlling the rate of vaporization of mercury in a reservoir communicating with the lamp envelope through a narrow passage. The escape of mercury from the lamp envelope is prevented during sealofl by quickly reducing the pressure of the mercury vapor below atmosphere pressure and then immediately sealing the envelope. The narrow passage is elfective for slowing the flow of mercury from the envelope prior to scaling and this passage may be closed by a needle valve after the filling of the envelope is completed and before the vapor pressure in the envelope is reduced.

In the drawing accompanying and forming part of this specification, two species of apparatus for filling lamp envelopes with mercury are shown in which:

Fig; 1 is a schematic representation of a lamp on velope and an apparatus useful for distilling mercury into the lamp envelope,

Fig. 2 is a similar illustration of a lamp envelope and another apparatus useful for distilling mercury into the lamp envelope, and

Fig. 3 is a similar illustration of a lamp envelope having an exhaust tubulation provided with a branch.

Referring to Fig. l of the drawing the lamp envelope is shown at 1 and is in the form of a quartz arc tube having a pair of main discharge supporting electrodes 2 and 3 sealed into its ends and an auxiliary starting electrode 4 sealed into one end. In the 400 watt commercial lamp the arc tube 1 is approximately 4 /2 inches long and /4 inch in outer diameter and the main discharge supporting electrodes 2 and 3 are made up of a pencil of thorium in a tungsten wire coil. In the actual lamp the arc tube 1 is mounted in a glass envelope provided with a conventional screw base and the tube is supported within the envelope and supplied with electrical energy by metal support members, as is well known.

As shown in the drawing the arc tube 1 is provided with two exhaust tubulations 5 and 6 extending in opposite directions. The upper tubulation 5 is used to connect the tube 1 to an exhaust system and to a source of rare gas in the usual manner. The lower tubulation 6 is connected to a line elongated quartz capillary tube 7 opening into a quartz bulb 8 or reservoir containing liquid mercury 9. The capillary tube 7 is suitably about 6 inches long with a bore of about 5 to 10 mils. A tubular electric furnace or oven 10 is mounted around the capillary tube 7 and another electric furnace 11 is mounted around the bulb 8 and telescoped slightly with in the furnace 10. The furnace 10 is connected with a power source which supplies electrical energy thereto at a rate sufficient to maintain the capillary tube 7 at a temperature of about 550 C. to prevent any condensation of mercury in the capillary tube. The furnace 11 is connected with a power source through means capable of varying and accurately controlling the power supplied to the furnace. The mercury vapor pressure in the system including the arc tube 1 can thus be controlled by changing the rate at which power is supplied to the furnace 11.

In filling the arc tube 1 with the proper amount of mercury vapor to obtain a predetermined lamp operating voltage, the tube 1 and the exhaust tribulations 5 and 6 are first heated, suitably by a torch, while the exhaust system is connected to the upper tubulation 5 to remove occluded and other gases from the tube 1. Of course, the capillary tube 7 and the bulb 8 communicating with the arc tube 1 are also exhausted of gases at this time and preferably the furnaces 10 and 11 are energized during this period though the temperature of the furnace 11 around the bulb 8 is kept at a low heat to avoid vaporizing an appreciable amount of the mercury 9.

After the exhaust step has been completed an ionizable gas, preferably argon at about 25 mm. pressure, is introduced into the arc tube 1 through the tubulation and a discharge is operated between the main electrodes 2 and 3 to degas them. The are tube 1 is then again exhausted, then refilled with the ionizable gas and a discharge is again established between the main electrodes. This is usually sufficient to thoroughly degas the electrodes 2 and 3 and after again exhausting the arc tube 1 and refilling it with the ionizable gas the tubulation 5 is sealed off from the exhaust system by fusing its walls together close to the tube 1 in the usual manner.

The mercury vapor is then introduced into the arc tube 1 by starting and operating a discharge in the tube 1 and, with the discharge operating, the power supplied to the furnace 11 is increased to raise the temperature of the bulb 8 and increase the rate of vaporization of the mercury in the bulb. The mercury vapor passes through the capillary tube 7 into the arc tube 1 and as the pressure thereof gradually increases the operating voltage of the discharge in the arc tube 1 also gradually increases. The rise in voltage can be made very gradual as it approaches the desired predetermined value by controlling the current supplied to the furnace 11 around the bulb 8.

When the operating voltage of the discharge has attained the desired value, which is 135 volts in the 400 watt lamp, the power is cut off from the arc tube 1 and the furnace 11. The arc tube 1 is then immediately cooled rapidly, as by a cold air stream or a wet asbestos sponge, to reduce the pressure of the atmosphere therein to below atmospheric pressure. The furnace 10 around the capillary tube 7 is then lowered slightly to permit sealing-off the exhaust tubulation 6 by a pointed flame directed at a part thereof as close as possible to the arc tube 1. This is done as soon as the pressure in the arc tube 1 drops below atmospheric. Lowering the pressure of the arc tube atmosphere below atmospheric pressure is necessary to avoid blowing out of the exhaust tubulation 6 when the latter is heated by the flame in sealing it ofi from the capillary tube.

The small bore capillary tube 7, by slowing substantially the rate at which mercury vapor flows between the interior of the arc tube 1 and the interior of the bulb 8 under the effect of a pressure differential in these spaces, makes it possible to reduce the vapor pressure in the arc tube to below atmospheric pressure so that the exhaust tubulation may be sealed in the above manner without blowing it out and while avoiding either an I increase or a decrease in the amount of mercury present in the arc tube 1 when the desired predetermined operating voltage was attained. Of course, the difference in the vapor pressure in the arc tube 1 and in the bulb 8 is preferably as small as possible while the arc tube is being cooled from its operating temperature to the temperature at which the pressure of the vapor therein is below atmospheric pressure and until the tubulation 6 is sealed-off. Usually cutting off the power to the furnace 11 while cooling the tube 1 is sufficient, though forced cooling of the bulb 8 may be resorted to, when desired.

After the exhaust tubulation 6 has been sealed-off the arc tube 1 is ready for mounting in the glass envelope of the lamp and has the same predetermined operating voltage as it had prior to sealing tubulation 6.

The apparatus shown in Fig. 2 is similar to that shown in Fig. 1 and the operation is similar but in this apparatus the narrow bore tube 12 is shorter and of larger bore, about mils, and a magnetically controlled needle valve 13 is provided to shut the passage through the tube 12. This arrangement allows quicker filling of the arc tube 1 with mercury vapor due to the larger passage through the tube 12 and a positive closing of the passage between the bulb 8 and the arc tube 1 when the desired operating voltage has been attained.

The engaging conical surfaces of the needle valve are polished to make a close fit with each other and the needle 13 of iron or tungsten, for example, is attached to an iron cylinder 14 within the quartz tube 15. A quartz stop 16 is provided in the tube 15 for the needle 13, 14 and the usual solenoid coil 17 surrounds the furnace 18. The arrangement of the coil 17 and the cylinder 14 is such that the needle valve is closed on energization of the coil 17. A small movement of about 2 mm. for the needle is satisfactory.

A torch 18 is directed so as to play a soft flame on the portion of the tubulation 6 extending between the tube 12 and the arc tube 1 to avoid condensation of mercury vapor therein. A second torch 19 is directed and arranged to play when ignited a sharp flame on the portion of the tubulation to be sealed.

The procedure is the same as described in connection with Fig. 1 except that when the desired operating voltage of the arc tube has been attained the coil 17 is energized to shut the valve 12, 13, 14. After the operation of the discharge in the arc tube has been interrupted and the tube 1 cooled to reduce the pressure therein to below atmospheric pressure the torch 19 is ignited to seal the tubulation 6. The mercury thus sealed in the tube 1 is that amount required for the desired predetermined operating voltage of the arc tube 1.

The apparatus of Fig. 2 is particularly useful for accurately filling arc tubes of small sizes such as those for lamps designated commercially as the W l i-4.

In filling arc tubes by the above described apparatus and procedures all parts of the arc tube 1 and the tubulation 6 confining the mercury vapor should be above the temperature at which mercury would condense thereon while the arc tube 1 is being filled with vapor and until the seal-off is made in the tubulation.

The double tubulation 20 shown in Fig. 3 is useful in the apparatus of Figs. 2 and 3 and results in a single seal-off tip on the arc tube 1.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An apparatus for filling the quartz arc tubes of high pressure mercury vapor lamps with an exact amount of mercury vapor sufiicient only to produce a vapor pressure above atmospheric pressure and a predetermined operating arc tube voltage, comprising a quartz reservoir for liquid mercury, an elongated quartz tube having a small bore and connected to conduct mercury vapor from said reservoir into the interior of the are tube, a furnace around said elongated tube including means to maintain the temperature of the elongated tube above the condensation temperature of mercury vapor at a vapor pressure corresponding to a predetermined arc tube operating voltage another furnace around said reservoir to cause vaporization of the mercury therein, and means to control and gradually increase the temperature of said second furnace to control the rate of vaporization of mercury in said reservoir whereby to gradually increase the mercury vapor pressure in said are tube during operation of said are tube to a value corresponding to the predetermined arc tube operating voltage, the bore of said elongated tube being restricted to a size effective for retarding the flow of mercury vapor therethrough whereby on attaining said predetermined arc tube voltage the mercury vapor pressure in said are tube may be quickly reduced below atmospheric pressure and said are tube then s aled off from said elongated tube and said reservoir without loss of mercury from said are tube.

2. An apparatus for filling the quartz arc tubes of high pressure mercury vapor lamps with an exact amount of mercury vapor sufiicient only to produce a vapor pressure above atmospheric pressure and a predetermined operating arc tube voltage comprising a quartz reservoir for liquid mercury, an elongated quartz tube having a small bore and. connected to conduct mercury vapor from said reservoir into the interior of the arc tube, a magnetically controlled needle valve in said elongated tube, a furnace around said elongated tube including means to maintain the temperature of the elongated tube above the condensation temperature of mercury vapor at a vapor pressure corresponding to a predetermined arc tube operating voltage, another furnace around said reservoir to cause vaporization of the mercury therein and means to control and gradually increase the temperature of said second furnace to control the rate of vaporization of mercury in said reservoir whereby to control and gradually increase the mercury vapor pressure in said arc tube during operation of the arc tube to a value corresponding to the predetermined arc tube operating voltage and whereby on closing of said needle valve on attaining said predetermined arc tube voltage, the mercury vapor pressure in said are tube may be quickly reduced below atmospheric pressure and said are tube then sealed off from said elongated tube and said reservoir without loss of mercury from said are tube.

3. The method of introducing mercury into an arc tube suflicient only in amount to produce a predetermined arc tube operating voltage corresponding to a mercury vapor pressure higher than atmospheric pressure which comprises the steps of connecting the interior of the arc tube containing an ionizable gaseous atmosphere to a reservoir of mercury through a narrow passage to form a hermetically closed system, operating an electric discharge in said are tube to raise the arc tube temperature above the condensation temperature of mercury vapor at a vapor pressure corresponding to a predetermined arc tube operating voltage, heating the walls of said passage to a corresponding temperature and, while continuing the aforesaid heating of said passage walls and the operation of said are tube, heating the mercury in said reservoir to gradually increase its temperature sufficiently to produce first a pressure differential between the interior of said are tube and the interior of said reservoir, then a consequent flow of mecury vapor from said reservoir through said passage and into said are tube and then an increase in the pressure of mercury vapor in said are tube to increase the operating voltage of said are tube, continuing the aforesaid heating of the mercury in said reservoir and the other parts of said system to gradually increase the pressure of mercury vapor in said are tube until the aforesaid predetermined arc tube operating voltage is attained, then stopping the flow of mercury vapor into said are tube and with the mercury vapor fiow stopped rapidly cooling said are tube by interrupting the discharge and applying a coolant to the arc tube wall to quickly reduce the pressure of the mercury vapor therein to below atmospheric pressure and then immediately sealing oil said are tube from said passage to retain in said tube an amount of mercury sutlicient only to produce the aforesaid predetermined operating voltage of the arc tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,228,327 Spanner Ian. 14, 1941 2,284,036 801 May 26, 1942 2,311,930 Chirelstein Feb. 23, 1943 2,456,396 Frohock Dec. 14, 1948 

3. THE METHOD OF INTRODUCING MERCURY INTO AN ARC TUBE SUFFICIENT ONLY IN AMOUNT TO PRODUCE A PREDETERMINED ARC TUBE OPERATING VOLTAGE CORRESPONDING TO A MERCURY VAPOR PRESSURE HIGHER THAN ATMOSPHERIC PRESSURE WHICH COMPRISES THE STEPS OF CONNECTING THE INTERIOR OF THE ARC TUBE CONTAINING AN IONIZABLE GASEOUS ATMOSPHERE TO A RESERVOIR OF MERCURY THROUGH A NARROW PASSAGE TO FORM A HERMETICALLY CLOSED SYSTEM, OPERATING AN ELECTRIC DISCHARGE IN SAID ARC TUBE TO RAISE THE ARC TUBE TEMPERATURE ABOVE THE CONDENSATION TEMPERATURE OF MERCURY VAPOR AT A VAPOR PRESSURE CORRESPONDING TO A PREDETERMINED ARC TUBE OPERATING VOLTAGE, HEATING THE WALLS OF SAID PASSAGE TO A CORRESPONDING TEMPERATURE AND, WHILE CONTINUING THE AFORESAID HEATING OF SAID PASSAGE WALLS AND THE OPERATION OF SAID ARC TUBE, HEATING THE MERCURY IN SAID RESERVOIR TO GRADUALLY INCREASE ITS TEMPERATURE SUFFICIENTLY TO PRODUCE FIRST A PRESSURE DIFFERENTIAL BETWEEN THE INTERIOR OF SAID ARC TUBE AND THE INTERIOR OF A RESERVOIR, THEN A CONSEQUENT FLOW OF MERCURY VAPOR FROM SAID RESERVOIR THROUGH SAID PASSAGE AND INTO SAID ARC TUBE AND THEN AN INCREASE IN THE PRESSURE OF MERCURY VAPOR IN SAID ARC TUBE TO INCREASE THE OPERATING VOLTAGE OF SAID ARC TUBE CONTINUING THE AFORESAID HEATING OF THE MERCURY IN SAID RESERVOIR AND THE OTHER PARTS OF SAID SYSTEM TO GRADUALLY INCREASE THE PRESSURE OF MERCURY VAPOR IN SAID ARC TUBE UNTIL THE AFORESAID PREDETERMINED ARC TUBE OPERATING VOLTAGE IS ATTAINED, THEN STOPPING THE FLOW OF MERCURY VAPOR INTO SAID ARC TUBE AND WITH THE MERCURY VAPOR FLOW STOPPED RAPIDLY COOLING SAID ARC TUBE BY INTERRUPTING THE DISCHARGE AND APPLYING A COOLANT TO THE ARC TUBE WALL TO QUICKLY REDUCE THE PRESSURE OF THE MERCURY VAPOR THEREIN TO BELOW ATMOSPHERIC PRESSURE AND THEN IMMEDIATELY SEALING OFF SAID ARC TUBE FROM SAID PASSAGE TO RETAIN IN SAID TUBE AN AMOUNT OF MERCURY SUFFICIENT ONLY TO PRODUCE THE AFORESAID PREDETERMINED OPERATING VOLTAGE OF THE ARC TUBE. 